I have an external HDD which I leave attached to my MacBook Pro for most of the time.
Sometimes when the system is slow to response to a UI action, I notice that the MacBook is taking time to whir the external drive back up. This is for operations where I think OS X doesn't need to use the HDD.
Is anyone able to clarify why one might see slow/delayed responses at times to some UI actions on a MacBook whilst the external drive is attached? Is there something I can do to minimize the times where Mac OS will want all drives (i.e. including external storage HDDs) up and spinning?